With the increased popularity of mobile terminals, data traffic has been increasing. In order to support the increased data traffic, a carrier aggregation mobile station (CA MS) concurrently using a primary cell (P cell) and a secondary cell (S cell), each using a different carrier frequency, has been provided. CA is a service suitable to MSs that heavily rely upon data traffic. Particularly, the Release 10 TS36.300 Annex. J introduces various scenarios applicable to the CA MS.
For example, a co-located scenario of maximizing a data throughput by superposing frequency zones of a P cell and an S cell has been suggested. However, making the frequency zones of the P cell and S cell coincident with each other is merely an ideal scenario and, in reality, it is difficult to perfectly make the frequency zones of the P cell and the S cell coincident with each other. To make the inconsistent frequency zones of the P cell and the S cell coincident with each other, much time is required. Although much time is spent and the frequency zones of the P cell and the S cell are adjusted, it is almost impossible to make the two frequency zones physically perfectly coincident with each other.
If the frequency zones of the P cell and the S cell do not coincide with each other, a situation may occur in which, because a CA MS supporting CA receives a weaker signal than a non-CA MS not supporting CA, the CA MS has a lower data throughput than the non-CA MS.
For example in the related art, as illustrated in FIG. 1, in a situation in which the frequency zones of the P cell and S cell do not coincide with each other, the CA MS may use a P1 cell as the P cell, and use a B cell as the S cell. At this time, the P cell and the S cell may be in a state of being previously matched in a form of P0 and A, P1 and B, and P2 and C by the co-located scenario. The CA MS in the illustrated position performs no handover, because signal reception from the B cell being the S cell is almost impossible and a received signal strength from the P1 cell being the P cell is not as weak as the CA MS. That is, it may not be possible for the CA MS in the illustrated position to receive a signal from the B cell in a state where a signal reception condition of the P1 cell is not so good, whereas the non-CA MS in the same position may perform handover to the C cell and receive a strong signal from the C cell. As a result, a situation may occur in which the CA MS has a worse signal transmission/reception efficiency than the non-CA MS.
In accordance with this, there is a need to provide a technology in which the CA MS using all of the P cell and the S cell can more rapidly perform a handover to a cell of a good channel condition, so as to always maintain a higher data rate than the non-CA MS.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.